Cancer is a major cause of human death. There is currently no cure for many types of human cancers. Many cancers are very aggressive with a high mortality and some have an increasing incidence in recent years. For example, melanoma is a common skin cancer and recent decades have seen a markedly increase in its incidence worldwide (Jemal A, Devesa S S, Hartge P, Tucker M A. Recent trends in cutaneous melanoma incidence among whites in the United States. J Natl Cancer Inst 2001; 93:678-83; Lasithiotakis K G, Leiter U, Gorkievicz R, et al. The incidence and mortality of cutaneous melanoma in Southern Germany: trends by anatomic site and pathologic characteristics, 1976 to 2003. Cancer 2006; 107:1331-9; Ries L A G, Melbert D, Krapcho M, et al. (eds). SEER Cancer Statistics Review, 1975-2005, National Cancer Institute. Bethesda, Md., http://seer.cancer.gov/csr/1975_2005/, based on November 2007 SEER data submission, posted to the SEER web site, 2008). In the United States alone, 62,480 new cases and 8,420 deaths from melanoma were estimated for the year of 2008 (Ries, supra). Although early-stage disease is curable through surgical excision, advanced metastatic melanoma is resistant to current treatments, with a rapidly progressive course and high mortality rate (Flaherty Ky. Chemotherapy and targeted therapy combinations in advanced melanoma. Clin Cancer Res 2006; 12:2366s-70s; Tawbi H A, Kirkwood J M. Management of metastatic melanoma. Semin Oncol 2007; 34:532-45).
A major effort in melanoma research has thus been to identify novel treatment strategies targeting major molecular pathways, particularly the Ras→Raf→MEK→MAP kinase/ERK (MAPK) and PI3K/Akt signaling pathways, which are commonly over-activated by genetic alterations, such as the BRAF mutations in the MAPK pathway (Davies H, Bignell G R, Cox C, et al. Mutations of the BRAF gene in human cancer. Nature 2002; 417:949-54) and the PIK3CA amplification and PTEN mutations in the PI3K/Akt pathway (Wu H, Goel V, Haluska F G. PTEN signaling pathways in melanoma. Oncogene 2003 22:3113-22; Curtin J A, Fridlyand J, Kageshita T, et al. Distinct sets of genetic alterations in melanoma. N Engl J Med 2005; 353:2135-47; Marquette A, Bagot M, Bensussan A, Dumaz N. Recent discoveries in the genetics of melanoma and their therapeutic implications. Arch Immunol Ther Exp (Warsz) 2007; 55:363-72). These two pathways play a fundamental role in the pathogenesis and progression of melanoma and are therefore important therapeutic targets for this cancer (Satyamoorthy K, Li G, Gerrero M R, et al. Constitutive mitogen-activated protein kinase activation in melanoma is mediated by both BRAF mutations and autocrine growth factor stimulation. Cancer Res 2003; 63:756-9; Stahl J M, Sharma A, Cheung M, et al. Deregulated Akt3 activity promotes development of malignant melanoma. Cancer Res 2004; 64:7002-10; Dai D L, Martinka M, Li G. Prognostic significance of activated Akt expression in melanoma: a clinicopathologic study of 292 cases. J Clin Oncol 2005; 23:1473-82; Meier F, Schittek B, Busch S, et al. The RAS/RAF/MEK/ERK and PI3K/AKT signaling pathways present molecular targets for the effective treatment of advanced melanoma. Front Biosci 2005; 10:2986-3001; Meier F, Busch S, Lasithiotakis K, et al. Combined targeting of MAPK and AKT signalling pathways is a promising strategy for melanoma treatment. Br J Dermatol 2007; 156:1204-13; Kwong L, Chin L, Wagner S N. Growth factors and oncogenes as targets in melanoma: lost in translation? Adv Dermatol 2007; 23:99-129).
Radioiodine therapy based on the sodium/iodide symporter (NIS) gene transfer has been widely investigated as a potential therapeutic strategy for extrathyroidal malignancies (Faivre J, Clerc J, Gérolami R, et al. Long-term radioiodine retention and regression of liver cancer after sodium iodide symporter gene transfer in Wistar rats. Cancer Res 2004; 64:8045-51; Dwyer R M, Bergert E R, O'connor M K, et al. In vivo radioiodide imaging and treatment of breast cancer xenografts after MUC1-driven expression of the sodium iodide symporter. Clin Cancer Res 2005; 11:1483-9; Riesco-Eizaguirre G, Santisteban P. A perspective view of sodium iodide symporter research and its clinical implications. Eur J Endocrinol 2006; 155:495-512; Schipper M L, Riese C G, Seitz S, et al. Efficacy of 99mTc pertechnetate and 131I radioisotope therapy in sodium/iodide symporter (NIS)-expressing neuroendocrine tumors in vivo. Eur J Nucl Med Mol Imaging 2007; 34:638-50; Willhauck M J, Sharif Samani B R, Klutz K, et al. Alpha-fetoprotein promoter-targeted sodium iodide symporter gene therapy of hepatocellular carcinoma. Gene Ther 2008; 15:214-23). NIS is normally expressed in the basal membrane of follicular thyroid cells, which transports iodide from blood stream into the cell for the biosynthesis of thyroid hormone (Riesco-Eizaguirre, supra; Nilsson M. Iodide handling by the thyroid epithelial cell. Exp Clin Endocrinol Diabetes 2001; 109:13-17). This process also involves several other key molecules, including thyroglobulin (Tg), which incorporates iodide through organification that involves thyroperoxidase (TPO). Thyroid transcription factor 1 (TTF1 or TITF1) and 2 (TTF2 or FOXE1) and PAX8 are involved in the regulation of these genes. Expression of many of these iodide-handling genes in the thyroid cell is up-regulated by the thyroid-stimulating hormone (TSH), which acts on the TSH receptor (TSHR) in the thyroid cell membrane. This is the molecular basis for the commonly used radioiodide ablation therapy for thyroid cancer, which is clinically facilitated by increasing the level of TSH in the blood of the patient either through thyroid hormone withdrawal or administration of recombinant human TSH (Mian C, Lacroix L, Bidart J.-M, Caillou B, Filetti S, Schlumberger M. Sodium/iodide symporter in thyroid cancer. Exp Clin Endocrinol Diabetes 2001; 109: 47-51; Duntas L H, Cooper D S. Review on the occasion of a decade of recombinant human TSH: prospects and novel uses. Thyroid 2008; 18(5):509-16). In papillary thyroid cancer (PTC), BRAF mutation (and hence activation of the MAPK pathway) was associated with decreased radioiodine avidity (Xing M, Westra W H, Tufano R P, et al. BRAF mutation predicts a poorer clinical prognosis for papillary thyroid cancer. J Clin Endocrinol Metab 2005; 90:6373-9; Riesco-Eizaguirre G, Gutierrez-Martinez P, Garcia-Cabezas M A, Nistal M, Santisteban P. The oncogene BRAF V600E is associated with a high risk of recurrence and less differentiated papillary thyroid carcinoma due to the impairment of Na+/I− targeting to the membrane. Endocr Relat Cancer 2006; 13:257-69; Mian C, Barollo S, Pennelli G, et al. Molecular characteristics in papillary thyroid cancers (PTCs) with no (131)I uptake. Clin Endocrinol 2008; 68:108-16), which can be explained by BRAF mutation-associated silencing of thyroid iodide-handling genes, such as NIS (Riesco-Eizaguirre G, Santisteban P, supra; Durante C, Puxeddu E, Ferretti E, et al. BRAF mutations in papillary thyroid carcinomas inhibit genes involved in iodine metabolism. J Clin Endocrinol Metab 2007; 92:2840-3), Tg (Durante, supra), and TPO (Mian, supra; Durante, supra; Giordano T J, Kuick R, Thomas D G, et al. Molecular classification of papillary thyroid carcinoma: distinct BRAF, RAS, and RET/PTC mutation-specific gene expression profiles discovered by DNA microarray analysis. Oncogene 2005; 24:6646-56; Di Cristofaro J, Silvy M, Lanteaume A, Marcy M, Carayon P, De Micco C. Expression of tpo mRNA in thyroid tumors: quantitative PCR analysis and correlation with alterations of ret, Braf, ras and pax8 genes. Endocr Relat Cancer 2006; 13:485-95). Several previous studies also demonstrated involvement of the PI3K/Akt pathway in the regulation of thyroid iodide-handling genes. For example, expression of a mutant Ras that selectively stimulated the PI3K/Akt pathway markedly decreased TSH-induced NIS expression (Cass L A, Meinkoth J L. Ras signaling through PI3K confers hormone-independent proliferation that is compatible with differentiation. Oncogene. 2000; 19:924-32) and IGF-I could inhibit cAMP-induced NIS expression through activating the PI3K/Akt pathway (Garcia B, Santisteban P. PI3K is involved in the IGF-I inhibition of TSH-induced sodium/iodide symporter gene expression. Mol Endocrinol 2002; 16:342-52) in thyroid cells.
In recent clinical trials on various human cancers, including melanoma, targeting an individual pathway, such as the MAPK pathway or the PI3K/Akt pathway, or use of a single agent generally failed to show significant clinical responses (Marquette, supra; Kwong, supra; Friday B B and Adjei A A. Advances in targeting the Ras/Raf/MEK/Erk mitogen-activated protein kinase cascade with MEK inhibitors for cancer therapy. Clin Cancer Res 2008; 14:342-6). A recent study showed common expression of TSHR in melanoma cells, but no or little expression in benign skin lesions (Ellerhorst J A, Sendi-Naderi A, Johnson M K, Cooke C P, Dang S M, Diwan A H. Human melanoma cells express functional receptors for thyroid-stimulating hormone. Endocr Relat Cancer 2006; 13:1269-77), raising the possibility that other thyroid iodide-handling genes might also be expressible in melanoma cells.
There is a continuing need in the art to develop more effective treatments for human cancers.